The Adorable Bug-bear

The autumnal equinox has passed, leaves are starting to turn,
and throughout the country woolly bears are running rampant across streets and
sidewalks, sensing in their fuzzy little bodies the urge to pack on fat before
the cold sets in. They appear blind and brazen in their search for food,
conspicuously traveling by day, traversing heavily-trafficked footpaths with
reckless abandon, all the while humping along at a scorching 0.045 miles per
hour. Polyphagous herbivores, woolly bears eat just about anything grown from
the ground with chlorophyll in it. Variety, it’s been said, is the spice of
life, and the bears go to great lengths to find it.

Generally, woolly
bears seen in Oregon are larvae of the Isabella tiger moth (Pyrrartica
Isabella), but the name “woolly bear” is often used to describe larvae of any
number of Arctiid species, a diverse moth family of which there are more than
11,000 species worldwide. Arctiid larvae have the interesting distinction of
being far more widely-known than their adult forms—everybody can identify a woolly
bear, but scant few have seen or even heard of the resultant moths. Indeed, the
fact that tiger moth larvae are called “woolly bear caterpillars” and not
simply “tiger moth larvae” only widens the disconnect. But in a way, it makes a
lot of sense: The larvae are diurnal, relatively long-lived, and often brightly
colored, whereas the imagoes are nocturnal, ephemeral, and cryptically shaded.
The caterpillars are the visible stage of its life cycle, eating, creeping, and
bumbling about; the adults work undercover, behind the scenes. Banded orange
and black, covered in soft bristles, the itinerant woolly bear is
also cute, a quality few moths can be said to possess.

There is a great
deal of folklore surrounding the woolly bear, centered on its purported ability
to forecast winter weather. A vaguely scientific study conducted from 1948 to
1956 by a Dr. C. H. Curran in New York attempted to prove that wider bands of orange
(the caterpillar’s middle segment) signaled a mild oncoming winter, while
narrow orange bands corresponded to harsher weather. He collected “as many
caterpillars as he could in a day” from Bear Mountain State Park each fall for
eight years, collating the data and offering to forecast the winter weather for
a reporter friend at The New York Herald Tribune. His predictions bore
out, more or less, though he himself acknowledged the small sample size and
admitted that the trips to the park “were simply an excuse for having fun.”
Curran, his wife, and their group of friends gamboled in the woodlands of
southeast New York, fancying themselves “The Original Society of the Friends of
the Woolly Bear”. Most scientists discount the theory—sample size being the big
sticking point—but at least one believes that a link between the bands and
winter severity is plausible.

“There’s evidence
that the number of brown hairs has to do with the age of the caterpillar—in
other words, how late it got going in the spring,” said Mike Peters, an
entomologist formerly of the University of Massachusetts, in 1999. “The
[band] does say something about a heavy winter or an early spring.
The only thing is, it’s telling you about the previous year.” Sort of
like looking at the width of tree rings to distinguish good growth years
(likely due to lots of rain) from bad, dry ones. But unlike trees, which last
for centuries in the right conditions, caterpillars tend to decompose rather
quickly—not the most useful long-term metereological metric.

While woolly bears
likely aren’t smarter than the average ursine bear—what with their
pinhead-sized brains—they do appear to exhibit a behavior more often associated
with “higher” species: self-medication. A study by researchers at Wesleyan
University found that the caterpillars of another Arctiid species (not the
Isabella), when infected with wasp larvae, seek out and devour more
alkaloid-rich plant matter than non-infected caterpillars, in an apparent
attempt to kill the parasites growing within them. Some background: Many
Arctiids are parasitized by flies and ichneumon wasps, which sting or otherwise
subdue the caterpillars before laying eggs on them. The larvae emerge, burrow
into the caterpillar, and essentially eat the host alive from the inside out.
(Sound cruel? Darwin, in 1860, thought so as well: “I cannot persuade myself
that a beneficent and omnipotent God would have designedly created the
Ichneumonidae with the express intention of their feeding within the living
bodies of caterpillars…”) The woolly bears, seemingly unsatisfied with this
arrangement, dose themselves with pyrrolizidine alkaloids to fight back, but
it’s a risky maneuver: alkaloids are toxic even to the caterpillar, and too
high a dose often ends up killing the host. What makes this finding all the
more remarkable is that, unlike humans and other primates that self-medicate,
these woolly bears are doing so without being taught. In other words, it
appears to be innate behavior, a built-in adaptation to an uncompromising
world.

For the next couple months the woolly bears will continue
ambling around, searching for food and, eventually, a place to hunker down and
pass the winter. Many Arctiid species can survive extremely low
temperatures—literally freezing solid without harm—thanks to substances called
cryoprotectants in their blood, which inhibit the growth of cell-rupturing ice
crystals. In the spring they’ll thaw out, pupate, and become moths for a
fleeting coda, the twilight of their days spent gallivanting in the moonshine.